This guide has now been updated to cover ALL wiis, 3.0-4.1 any region, and all LU64+ and foreign equivalents. (dunno about those Korean ones?)
LU64-65++ serial no. wiis still cannot downgrade their firmware - if you bought your wii this year then it most likely will be one, so don't downgrade it! You are safe to follow this guide though.
Make sure you do the steps in the right order or you could run into problems, and read the guide through a couple of times before trying it. Read ALL OF IT! Most problems arise from people not reading the instructions properly or not using a compatible SD card, a plain 2gb one is best.

All you need is an SD card formatted to FAT32, an internet connection and these files: _http://www.mediafire.com/?mvgnymjimmz

Before you start make sure Wiiconnect 24 is off as it can stop bannerbomb working, you may turn it back on once you have completed the guide.

If you get errors during any of the steps format your card with this tool.

TAKE OUT ALL GAMECUBE MEMORY CARDS/CONTROLLERS

1. INSTALL BOOTMII AND THE HOMEBREW CHANNEL

a). Put all the files from ‘copy to sd card.rar’ onto the root of the SD Card. It should look like this when done.

b). Insert the SD card into Wii.

c). Go to Wii Options, then go to Data Management > Channels > SD Card, then you will get a message saying "Load boot.elf?" , select 'Yes' and the Hackmii installer will run.

d). Install Bootmii as boot2 if you can, if not then install it as an IOS then go back and install the Homebrew Channel.

2. BACK UP YOUR NAND (OPTIONAL)

Making a NAND backup with Bootmii is highly recommended, it will recover your Wii from 99.9% of bricks.
Use the same SD card you used to install Bootmii and make sure there is at least 530mb free on it.
Bootmii is very fussy about what SD cards it uses, so avoid generic ones and try and use a Sandisk or similar.

a) Put the SD card into the Wii, if you installed Bootmii as boot2 then it will load, if it is installed as an IOS go to the Homebrew Channel, press 'home' on your wiimote and select 'Launch Bootmii'.

b) Use the power/reset/eject buttons to navigate the Bootmii menu and select the icon with the gears on it.

c) Now select the icon with a green arrow pointing from the chip to the SD card and follow the on screen instructions.

D) In about 10 mins you will have a NAND backup, it is normal to have up to 80 bad blocks so don't worry if you get some.

e) Put the SD card into PC and copy the NAND backup somewhere safe, you can now delete it from your card. If you installed Bootmii as boot2 then also copy the Bootmii folder to your PC and either delete or rename it, otherwise it will load every time you switch your Wii on.

If ever you get bricked then copy the bootmii folder and NAND backup onto your card, do steps a) & b) again, using Preloader to get to HBC if necessary, then select the icon with the arrow going from the SD card to the chip. It is not recommended to restore your NAND if you have Bootmii installed as an IOS.

3. GET A CIOS (v3-3.2 skip to step d)

You may want to check this video before you do this stage. The only difference is that you can select 'load IOS from SD card' instead of download from NUS.

a) Go to Homebrew channel and run Trucha Bug Restorer, load IOS36, press 1, read the warnings then select 'downgrade IOS15', select to load IOS from SD card then let it do its job, keep an eye on what it is doing and make sure you select 'load from sd card' when it asks & don't get any errors.

b) Run Trucha Bug Restorer again, this time select to load IOS15 on first screen using dpad left/right, then select the IOS36 menu & install patched (select 'yes' on all 3 patches) IOS36 to slot 36, again using IOS from SD card.

d) Run cIOS38 r14 installer, select IOS36 as the one it should use and then select wad install.

4. UPDATE YOUR SYSTEM MENU VERSION (OPTIONAL)

This step is optional, you may upgrade now if you wish, LU64+ owners cannot downgrade! but can upgrade if you want. If you want to update to 4.1 then make sure you have at least 250 blocks free or you will brick, install IOS60-patched first (step 5a), then run Firmware Updater 4.1. If you are on 3.3 or 3.4 then I strongly recommend updating as it is not advisable to install Preloader on these firmwares.

5. THE FINAL STEP

Preloader is also an optional install, if you don't want it just skip b & c, system menu hacks can be taken care of by Starfall (3.2) or startpatch (4), if you want them click my sig and have a look through my mediafire. There are no preloader hacks for 3.3/3.4 or jap wiis, either upgrade or use startpatch/change region if your wii is jap.

a) If you are on system menu 4/4.1 use Wad Manager with default settings (IOS249 & SD card) to install IOS60-patched.wad - make sure you do this before you install Preloader. If you installed it in step 4 then skip this part. Never uninstall IOS60! You will brick!!

b). Open the Homebrew Channel and load Preloader, press 1 to install. After install, your Wii should reboot and load the Preloader menu. If it doesn't, turn your wii off and on again whilst holding down reset and it will load the Preloader menu.

c) Select 'system hacks' in the Preloader menu, and enable the hacks that you want - 'skip disc update check' and the region free ones are all you need. Select 'save settings' and wait for confirmation message to display 'settings saved'. Press B to go back, and enter Settings. Set 'Autoboot: System Menu' using D-Pad, then select save settings. Press B to return to main Preloader menu.

d) In the Preloader menu select Homebrew Channel (if you didn't install Preloader then just open HBC as normal), run Wad Manager 1.4, use default settings (IOS249 & SD card) and install these wads from the 'wad' folder:

All done! You will now have the safety/hacks of Preloader & Bootmii, NeoGamma R7 backup loader that has 99% compatibility, cIOS249 r14, IOS38, 53 & 55 for newer games and IOS50 to help prevent disc update bricks. If you ever need to access Preloader's settings hold down 'reset' when switching your Wii on.
If you get the 'system files corrupted' screen don't panic, just reinstall preloader and if that doesn't fix it reinstall your current system menu with Wad Manager.

UPDATES

If you want to update your cIOS in the future or if you want to install a different one just run the installer and select ios249 as the one it should use, it will overwrite the old one so no need to uninstall. If you want to update Neogamma go to wii options > data management > channels and delete the old one first, then just install the new one with wad manager.
If you want more hacks for Preloader have a look at them here, and copy/paste them to your hacks.ini file. Make sure there is one blank line at the bottom.

Install the new cIOScorp 3.3 for DVDR loading through Disc Channel - (works on all wiis) - Download

Install the Internet Channel - NTSCU or PAL

Use your Wii as a media player with MPlayer CE & DVDX

Get some emulators for all your old favourites (better than vc except for N64)

DVD-R

You need to use either Verbatim DVD-R or Ritek G05 DVD-R for your games, other discs won't work.

CREDITS TO THE GUIDE: TheGRiM

hey

I did this step:

4. UPDATE YOUR SYSTEM MENU VERSION (OPTIONAL)

This step is optional, you may upgrade now if you wish, LU64+ owners cannot downgrade! but can upgrade if you want. If you want to update to 4.1 then make sure you have at least 250 blocks free or you will brick, install IOS60-patched first (step 5a), then run Firmware Updater 4.1. If you are on 3.3 or 3.4 then I strongly recommend updating as it is not advisable to install Preloader on these firmwares

And all the other stuff prior to this correctly, Thou i forgot too check the 250 blocks so when it try to install it gave me an error and rebooted, so i freed the 250 blocks and installed it again everything went great and i am now on 4.1E but now on the menu the homebrew channel doesnt work gives me a black screen also with bootmii the homebrew doesnt work (black screen also), what should i do ?

I dont think my wii is bricked since it starts fine, loads backups via the backup launcher channel so something is wrong with the homebrew channel.